Neutrino masses and cosmic radiation density: combined analysis

Abstract

Abstract. We determine the range of neutrino masses and cosmic radiation content allowed by the most recent CMB and large-scale structure data. In contrast to other recent works, we vary these parameters simultaneously and provide likelihood contours in the two-dimensional parameter space of N eff , the usual effective number of neutrino species measuring the radiation density, and m ν . The allowed range of m ν and N eff has shrunk significantly compared to previous studies. The previous degeneracy between these parameters has disappeared, largely thanks to the baryon acoustic oscillation data. The likelihood contours differ significantly if m ν resides in a single species instead of the standard case of being equally distributed among all flavors. For m ν = 0 we find 2.7 < N eff < 4.6 at 95% CL while m ν < 0.62 eV at 95% CL for the standard radiation content.

WMAP five-year constraints on lepton asymmetry and radiation energy density: implications for Planck

“…We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivity by the future Planck satellite will reduces the errors on ξ ν and Y p down to σ(ξ ν ) ≃ 0.089 (68% CL) and σ(Y p ) = 0.0133 (68% CL) respectively, values fully consistent with the BBN bounds on these parameters [12]. Our forecasted errors on the cosmological parameters from Planck-like simulated data are also consistent those obtained in Ref.…”

“…In particular, the non-zero neutrino chemical potential leads to changes in neutrino free-streaming length and neutrino Jeans mass due to the increase of the neutrino velocity dispersion [45,46]. After WMAP3 data release there are many works aiming to constrain N ef f from cosmological observations [14,34,37,47,48,49]. Their results suggest large values for N ef f within 95% CL interval, some of them not including the standard value 3.046 [14,34,37].…”

“…Such results have impact on cosmology because sterile neutrinos can contribute to the number of relativistic degrees of freedom at the Big Bang Nucleosynthesis [11]. These models are subject to strong bounds on the sum of active neutrino masses from the combination of various cosmological data sets [12,13], ruling out a thermalized sterile neutrino component with eV mass [14,15]. However, there is the possibility to accommodate the cosmological observations with data from short base-line neutrino oscillation experiments by postulating the existence of a sterile neutrino with the mass of few keV having a phase-space distribution significantly suppressed relative to the thermal distribution.…”

The cluster gas mass fraction as a cosmological probe: a revised study

“…All these densities are expressed in units of the critical density, ρ c = 3H 2 0 /(8πG), where H 0 is Hubble's constant and G is the gravitational constant. In our computation, we neglect (i) the energy associated with the cosmic radiation, Ω r ≈ 4.16 × 10 −5 (T CMB /2.726K) 4 ; and (ii) any possible contributions from light neutrinos, Ω ν h 2 70 = m ν /45.5 eV, that is expected to be less than 0.01 for a total mass in neutrinos, m ν , lower than 0.62 eV (see, e.g., Hannestad & Raffelt 2006). Therefore, we adopt the Einstein equation in the form Ω m + Ω Λ + Ω k = 1, where Ω k accounts for the curvature of space.…”

Observational bounds on the cosmic radiation density

“…This exercise has been performed by several groups before [3][4][5][6][7][8] and after [9][10][11][12][13][14][15] the release of the WMAP 3-year data [15][16][17]. Some of these recent results suggest surprisingly large values for N eff , with 95% C.L.…”